In all sorts of magnetic recording tapes used for sound recording, picture recording, computers, etc., the magnetic layers on their surfaces commonly tend to gradually wear because of their strongly close contact with magnetic heads, and also reproduction units or players trend toward compactness in size. For these reasons, thin types are presently demanded as magnetic recording mediums so that the mediums can travel without difficulty and also their manufacturing processes can be simplified.
Recently in particular, those of multiple layer structure, comprising a support and provided by coating thereon a magnetic layer and besides an intermediate layer, and magnetic recording mediums provided with a plurality of magnetic layers having different performances are on the market. However, the manufacturing processes for such magnetic recording mediums of multiple layer structure are complicated. In particular, the products tend to have poor magnetic characteristics, and also may cause a number of dropouts at the time of reproduction, resulting in a poorness in quality. The surface layers thereof also commonly tend to have a large thickness, because large-particle abrasives or the like are dispersed so that wear resistance can be imparted to the magnetic layer formed by uniformly dispersing ferromagnetic material powder in a binder.
In order to give good electromagnetic conversion characteristics, the component layer surface on the magnetic layer side must be processed to smoothness, so that the particle size of magnetic powder and fillers is selected and calendering is applied.
An excessive smoothness of the surface, however, may bring about an increase in coefficient of friction and a poorness of traveling performance. On the other hand, an excessive roughness of the surface may result in spacing loss, dusting, and unpleasant wear of heads.
The smoothness or roughness of the surface of the magnetic layer is therefore the subject that should be thoroughly studied. However, the surfaces of non-magnetic supports hitherto used in magnetic recording mediums (hereinafter generally referred to as magnetic tapes) have commonly a surface roughness that may incidentally bring about irregularities on the surfaces of the magnetic tapes to the extent that may give a problem from the viewpoint of the magnetic characteristics. Hence, also because most magnetic tapes having been put into practical use are comprised of a single magnetic layer, it does not result that such surface roughness can be absorbed even if some ordinary subbing layer is provided. This causes highly frequent occurrence of dropouts or the like.
It has been attempted to eliminate this difficulty by making a magnetic layer thick, but a low level of electromagnetic conversion characteristics can not be avoided because of the largness in thickness.